Methods for color and texture control of metallic glasses by the combination of blasting and oxidization

ABSTRACT

Methods of altering the surface of a metallic glass are provided. The methods include blasting and oxidation of a metallic glass surface, blasting a metallic glass surface using multiple shot media sizes, and thermal spray blasting a metallic glass surface with controlled cooling.

CROSS-REFERENCE TO RELATED PATENT APPLICATIONS

This patent application claims the benefit of U.S. Patent Application No. 62/235,072, entitled “Color and Texture Control of Metallic Glass Surfaces by the Combination of Blasting and Oxidization,” filed on Sep. 30, 2015 under 35 U.S.C. §119(e), which is incorporated herein by reference in its entirety.

This patent application also claims the benefit of U.S. Patent Application No. 62/265,866 under 35 U.S.C. §119(e), entitled “Surface Treatment with Thermal Spray Blasting to Control Appearance of Metallic glass Surfaces,” filed on Dec. 10, 2015, which is incorporated herein by reference in its entirety.

FIELD

The disclosure is directed to methods for providing surface treatment to control color and texture of metallic glass surfaces, and the resulting materials. More particularly, the embodiments relate to the surface treatment of metallic glass surfaces with the combination of blasting and oxidization, thermal spray blasting, and dissimilar shot media or blasting media.

BACKGROUND

Metallic glasses are metallic alloys that do not have a crystalline structure. Instead, like glass, their structure is amorphous. Metallic glasses have a number of material properties that make them viable for use in a number of engineering applications. Some of the properties of metallic glasses can include high strength, stiffness, toughness, corrosion resistance and processability from the molten state.

Casting metallic glasses can promote gas porosity and formation of surface features such as voids, crystals, and shedding parts on the metallic glass. Often such surface features are only visible after raw materials have been consumed and hours of manufacturing processes have been performed. Efforts have been made to manufacture metallic glasses having oxidized surfaces and textures and/or without certain surface features. However, there are limitations with current methods.

Metallic glasses typically do not have black surfaces. Further, as-cast metallic glass surfaces can include non-uniform surface features such as crystals, voids, shredding parts, flowlines, coldshuts, and misruns.

SUMMARY

The present disclosure provides methods of altering the surface of a metallic glass.

In certain aspects of the disclosure, methods include blasting and oxidation of a metallic glass surface. The metallic glass surface is blasted with shot media to form a porous blasted metallic glass surface. The porous blasted metallic glass surface has an oxidized layer. The porous blasted metallic glass surface is then oxidized, for example by annealing, to form a second oxidized layer thicker than the first oxidized layer. The blasting and oxidation steps can be repeated.

In another aspect, the methods include blasting a metallic glass surface using two different shot media sizes. A large shot media size can have an average diameter from 100 μm to 2000 μm. The fine shot media has an average diameter from 10 μm to 100 μm. In some variations, the large and fine shot media are used to blast the metallic glass surface simultaneously. In some aspects, the large shot media has particles that include a polymer base and a protruded sharp ceramic vertex.

In certain aspects of the disclosure, systems and methods for thermal spray blasting a metallic glass surface with controlled cooling. The metallic glass surface is blasted using a thermal spray gun with an integrated spray cooling in a flame nozzle. In various aspects, the thermal spray gun can be a high velocity oxygen fuel (HVOF) or high velocity air fuel (HVAF) thermal spray gun.

Additional embodiments and features are set forth in part in the description that follows, and will become apparent to those skilled in the art upon examination of the specification or can be learned by the practice of the disclosed subject matter. A further understanding of the nature and advantages of the present disclosure can be realized by reference to the remaining portions of the specification and the drawings, which forms a part of this disclosure.

BRIEF DESCRIPTION OF THE DRAWINGS

The description will be more fully understood with reference to the following figures and data graphs, which are presented as various embodiments of the disclosure and should not be construed as a complete recitation of the scope of the disclosure, wherein:

FIG. 1A illustrates blasting for controlling surface structure of a metallic glass before oxidization.

FIG. 1B shows a Ti-base metallic glass and a Zr-based metallic glass revealing flashing like a small firework.

FIG. 2A is a graph showing weight loss versus blasting time in a metallic glass resulting from blasting.

FIG. 2B is an optical photo of a metallic glass surface in an as-cast condition.

FIG. 2C is an optical photo of the metallic glass surface of FIG. 2B after blasting for 10 minutes.

FIG. 3 illustrates an exemplary process flow, including a first blasting followed by oxidization and a second blasting, and the respective surface features of metallic glasses.

FIGS. 4A-4D show optical images of a metallic glass (A) as-cast; (B) after a first blasting; (C) after oxidizing the first blasted surface; and (D) after a second blasting of the oxidized surface.

FIG. 5A shows an optical image of an oxidized Zr-based metallic glass surface without any blasting.

FIG. 5B shows a magnified optical image of FIG. 5A.

FIGS. 6A-6D show optical images of an outer appearance of the Zr-based metallic glass after (A) blast ZrO₂; (B) oxidization; (C) blasted after oxidization; and (D) oxidization again.

FIGS. 7A-D show optical photos illustrating that blasting and oxidization can eliminate crystals for the Zr-based metallic glass including (A) as-polished; (B) one minute ZrO₂ blast; (C) after oxidization; and (D) three minute ZrO₂ blast.

FIGS. 8A-D show optical photos illustrating the removal of micro-voids by blasting and oxidization of the Zr-based metallic glass including (A) as-polished; (B) one minute ZrO₂ blast; (C) after oxidization; and (D) three minute ZrO₂ blast.

FIGS. 9A-D show optical photos illustrating the healing of the contrast of shredding portions by blasting and oxidization of the Zr-based metallic glass including (A) as-polished; (B) one minute ZrO₂ blast; (C) after oxidization; and (D) three minute ZrO₂ blast.

FIG. 10A shows scanning electron microcopy (SEM) images of the microstructure of the oxide layer of the metallic glass formed after oxidization.

FIG. 10B shows microstructural analysis of the metallic glass of FIG. 10A by X-ray diffractometry.

FIG. 11A illustrates an example system for thermal spray blasting of a metallic glass surface with controlled cooling, according to an embodiment of the disclosure.

FIG. 11B illustrates example scan patterns of thermal spray blasting, with and without sample overrun, according to embodiments of the disclosure.

FIGS. 12A-12B illustrate example thermal spray blasting effects on metallic glasses, below and above Tg, according to embodiments of the disclosure.

FIGS. 13A-13D illustrate oxidized surface morphology of metallic glasses treated in accordance with an embodiment of the disclosure, and a comparative example of an oxidized surface morphology of a metallic glass treated with blasting and annealing.

FIG. 14 shows the surface structure of black Ni-based bulk metallic glass obtained by using a chemical etching treatment.

FIG. 15 illustrates desired blast shots for deep and sharp indentation on a sphere rubber base using a ceramic material (e.g. silicon carbide (SiC)) as a shot material.

FIG. 16A shows a SEM image of an outer appearance of a Zr-based metallic glass blasted by large shot media (e.g. Sirius #320).

FIG. 16B shows a back scattered electron (BSE) image of an outer appearance of a Zr-based metallic glass blasted by a first large shot media (e.g. Sirius #320).

FIG. 16C shows the surface structure and texture change versus gas pressures of the large shot media (e.g. Sirius #320) on a Zr-based metallic glass.

FIG. 17A shows an optical image of a metallic glass surface blasted by using large shot media (e.g. Sirius #320) and a depth profile of the metallic glass surface.

FIG. 17B shows a predicted cross-sectional image of the metallic glass blasted by using the large shot media (Sirius #320).

FIG. 18A shows an optical image of a blasted metallic glass surface blasted by using fine blast shot media (B505), and a corresponding depth profile on the metallic glass surface shown in the optical image of FIG. 18A.

FIG. 18B shows a predicted cross-sectional image of the metallic glass surface blasted by using the fine blast shot media (e.g. B505).

FIG. 19 shows a predicted metallic glass surface blasted by using a combination of the large shot (e.g. Sirius #320) and the fine blast shot (e.g. B505).

DETAILED DESCRIPTION

The disclosure can be understood by reference to the following detailed description, taken in conjunction with the drawings as described below. It is noted that, for purposes of illustrative clarity, certain elements in various drawings may not be drawn to scale.

The disclosure provides methods of a blasting metallic glass surfaces that can be used to control the surface color and texture. Blasted surfaces of metallic glasses are porous such that, in various embodiments, the blasted surfaces can provide uniform oxide growth to reduce spectacular light reflection and increases diffused reflection. Blasting also can remove surface features, such as crystals, voids, shredding parts, flowlines, and coldshuts, among others. In various aspects, oxidized surfaces can have a dark color and/or consistent texture.

In some embodiments, the metallic glass can have a consistent oxidized surface that exhibits surface roughness Rz equal to or less than 10 μm. In some embodiments, the metallic glass can have a consistent oxidized surface that exhibits surface roughness Rz equal to or less than 8 μm. In some embodiments, the metallic glass can have a consistent oxidized surface that exhibits surface roughness Rz equal to or less than 6 μm. In some embodiments, the metallic glass can have a consistent oxidized surface that exhibits surface roughness Rz equal to or less than 4 μm. In some embodiments, the metallic glass can have a consistent oxidized surface that exhibits surface roughness Rz equal to or less than 2 μm. In some embodiments, the metallic glass can have a consistent oxidized surface that exhibits surface roughness Rz equal to or greater than 1 μm. In some embodiments, the metallic glass can have a consistent oxidized surface that exhibits surface roughness Rz equal to or greater than 1.5 μm. In some embodiments, the metallic glass can have a consistent oxidized surface that exhibits surface roughness Rz equal to or greater than 2 μm. In some embodiments, the metallic glass can have a consistent oxidized surface that exhibits surface roughness Rz equal to or greater than 4 μm. In some embodiments, the metallic glass can have a consistent oxidized surface that exhibits surface roughness Rz equal to or greater than 6 μm. In some embodiments, the metallic glass can have a consistent oxidized surface that exhibits surface roughness Rz equal to or greater than 8 μm. In various aspects, a laser microscope can be used to measure the roughness of surface.

In various aspects, the methods described herein can produce metallic glass surfaces with various colors. An L*a*b* color space is a color space with dimension L* for lightness and dimensions a* and b* for color-opponent dimensions. Values of the L*a*b* color space are used for quantitative measurement of color change. The lightness, an L* value, represents the darkest black at L*=0, and the brightest white at L*=100. The color values a* and b* represent true neutral gray values at a*=0 and b*=0.

In various aspects, the color of the metallic glasses is darkened. In the L*a*b* color space, darker colors is characterized by lower L* values, and a* value and b* approaching zero. In other embodiment, the color can be grey or other colors. When diffusion reflection is reduced from a metallic glass surface, the L* value becomes lower.

Blasting and Oxidation for Color and Texture Control

In one aspect, the disclosure provides methods of blasting a surface of a metallic glass and subsequently oxidizing the metallic glass surface. In a first step, the metallic glass surface is blasted using blasting media. In a second step, the blasted metallic glass surface is oxidized.

FIG. 1A illustrates blasting for controlling surface structure of a metallic glass before oxidization. The initial texture of the metallic glass surface is machined or as-cast. As shown in FIG. 1A, shot media particles 102 are blasted over a top surface of a metallic glass, creating shear bands 106. Oxidization occurs after the first blasting step to form an oxidized metallic glass surface. On the right side of FIG. 1A, a treated surface 112 includes a consistent texture after a second blasting step that modifies the oxidized metallic glass surface.

In various aspects, blasting refers to forcibly propelling a stream of abrasive material against the metallic glass surface under high pressure. A pressurized fluid, such as compressed air, or a centrifugal wheel is used to propel the blasting material, which is often called the shot media. In various aspects, conventional blasting systems and methods can be used. For example, a Sirius processing and ultra-precision processing system by Fuji can be used.

The metallic glass can be blasted using any blasting media known in the art. The shot media generally includes ceramic, metal, glass, or polymer. It will be understood that any such blasting media known in the art can be used. In some embodiments, ceramic shot media such as zirconia beads (ZrO₂) (Saint Gobain B170) are used. In a particular embodiment, blasting can be performed using spheres of ZrO₂ (containing ˜30% SiO₂ and <10% Al₂O₃) incident on the metallic glass. With reference to FIG. 1B, blasting the surface of a metallic glass can cause the surface to flash like a small firework, indicated by arrow 116. The shot media 118 includes particles in a sphere shape. For example, when Zr-shot media is used on a Zr-based metallic glass, flashing can cause burning of the Zr metal on the Zr-based metallic glass surface and thus generate a high temperature at local area 110.

In various aspects, blasting the surface can remove a small amount of surface material from the surface of the metallic glass. In some aspects, at least 5 microns of metallic glass is blasted from the metallic glass surface during the blasting step. In some aspects, at least 10 microns of metallic glass is blasted from the metallic glass surface during the blasting step. In some aspects, at least 15 microns of metallic glass is blasted from the metallic glass surface during the blasting step. In some aspects, up to 20 microns is blasted from the surface.

The blasting step can reduce the weight of the metallic glass. An example of this weight loss during blasting is depicted in FIG. 2A. As shown, the weight loss increases with blasting time. The weight loss can be 0.12 g at a blasting time of 1200 seconds. For instance, a blasting period of ten minutes results in the weight loss of about 0.07 g, equivalent to removing 8 μm depth of the surface. In this example, the sizes of the blast shot media are between 45 to 100 μm and the blast has a low gas pressure of about 0.2 MPa.

FIG. 2B is an optical photo of an as-cast metallic glass surface. FIG. 2C is an optical photo of the metallic glass surface of FIG. 2B after 10 minutes of blasting, corresponding to a weight loss of 0.07 g. The resulting blasted surface, as shown in FIG. 2C, appears dark compared with the as-cast surface, as shown in FIG. 2B.

The amount of metallic glass surface material that can be removed during blasting can be increased based on the time of blasting, the intensity of the blast, the type of blasting media used, and other variables. The type of shot media impacting the surface, gas pressure of the blasting beam, size of a blasting shot media and blasting time, and other conditions known in the art can be altered. As the blasting time increases, more material will be removed from the metallic glass surface. In some aspects, the blasting time can be at least 300 seconds. In some aspects, the blasting time can be at least 600 seconds. In some aspects, the blasting time can be at least 900 seconds. In some aspects, the blasting time can be at least 1200 seconds. In some aspects, the blasting time can be at least 1500 seconds. In various aspects, and without limitation, the blasting time can be up to 1800 seconds or 30 minutes. Shorter blasting times result in more rapid processing.

The blasted surface can be plastically deformed to create shear bands. Without wishing to be held to a particular mechanism or mode of action, shear bands are stress induced shear deformed areas with lower density. The diffusibility in shear bands is high, and therefore oxidization of the metallic glass surface area can be accelerated. The blasting step provides a thin oxide layer on the metallic glass surface.

Blasting the metallic glass surface can modify the metallic glass surface before the subsequent oxidization step. The blasting step can create a porous structure on the metallic glass surface. The blasting step can promote formation of a thin oxide layer due to the high-energy produced at the metallic glass surface. Metallic glass surfaces are often coated with a hydroxide layer. Hydroxide can be formed on surface of a metallic glass in air atmosphere. For example, spray of cooling mist can lead to the formation of hydroxides, which generate a porous oxide layer on the surface of the metallic glass. The thickness of the oxide layer can be up to 1 micron, up to 2 microns, up to 3 microns, or up to 4 microns in thickness. The thin oxide layer can serve as a seeding layer for annealing to grow the oxidization layer into a thick oxidization layer in a second step. In various aspects, blasting can also remove surface features such as crystals, voids, shredding parts, flowlines, coldshuts, and misruns.

In a second step, the blasted surface is oxidized. Oxidation can be performed in any manner known in the art. In some aspects, metallic glass surfaces can be oxidized by heating the metallic glass to an elevated temperature for a period of time. In various aspects, the oxidation temperature can be at least 300° C. In various aspects, the oxidation temperature can be at least 350° C. In various aspects, the oxidation temperature can be at least 400° C. In various aspects, the oxidation temperature can be at least 450° C. In various aspects, the oxidation temperature can be at least 500° C. In various aspects, the oxidation temperature can be at least 550° C. In various aspects, the oxidation temperature can be at least 600° C. In various aspects, the oxidation time can be at least 10 minutes, at least 20 minutes, or at least 30 minutes. In some aspects, the oxidation time can range from 10 minutes to 30 minutes. Further, the temperature and oxidation time can vary. For example, the oxidation time can be shortened when the temperature increases and vice versa.

The oxidation step forms a thick oxidization layer on the metallic glass surface. In various aspects, the oxidation layer is at least 10 microns in thickness. In various aspects, the oxidation layer is at least 15 microns in thickness. In various aspects, the oxidation layer is at least 20 microns in thickness. In various aspects, the oxidation layer is at least 25 microns in thickness. In various aspects, the oxidation layer is at least 30 microns in thickness.

Without wishing to be limited to any mechanism or mode of action, the area of impact on the metallic glass surface can be a blast-impacted plastic deformed area. The blast-impacted plastic deformed area can contain a large number of shear bands on the metallic glass surface. The shear bands can act as a diffuse path of oxygen, and form micro-cracks in an oxide layer. Blasting can also cause oxidization of the metallic glass due to high-energy release at the surface area, and forms a thin oxide layer. After a separate oxidation step following the blasting step, the oxide layer can have an increased thickness, as well as a porous texture. The shear bands and micro-cracks can allow for increased absorbance of oxygen into the metallic glass. The blasting step can create a diffusion path and seed an oxide layer, while the oxidation step can grow the oxide layer to produce a thick oxidized surface over a large number of shear bands in the blast-impacted surface region.

The metallic glass can be any metallic glass known in the art. In various aspects, the metallic glass is a metallic glass that can oxidize. In some non-limiting aspects, the metallic glass can be Zr-based, Ti-based, Hf-based, and Nb-based, among others. The metallic glass can include one or more elements that oxidize. In one embodiment, the metallic glass is Zr-based. When the Zr-based metallic glass (e.g. the LM105 metallic glass) is used, a normal oxidized color is blue on the surface.

In various aspects, the combined blasting and oxidization on a metallic glass surface can form a darker color (e.g., grey or black) and a consistent texture surface (i.e. lack of variation in texture across the surface) on the metallic glass. FIG. 3 shows an example process that combines blasting and oxidization on a metallic glass surface resulting in a darker color and a consistent texture surface. As shown, after a first blasting step, shear bands 304 are created on a top surface of the metallic glass 302, and a thin oxide layer 310 is formed over shear bands 304. A second oxidizing step on the blasted surface produces a thick oxide layer 306 is formed over the shear bands 304 to form an oxidized surface. By using a second blasting step over the oxidized surface, the thick oxide layer 306 is removed and a microstructure/texture layer 308 is created on the top surface of the metallic glass 302. The microstructure/texture layer 308 is modified from the shear bands 304 by the second blasting step. The microstructure/texture layer 308 results in a darkened and/or consistent surface formed on the metallic glass. The metallic glass can thereby have an L* value under 50 in the L*a*b* color spectrum.

The steps of blasting and oxidizing can be repeated on the same surface. The second blasting step can provide for altered color and/or texture. FIGS. 4A-D show optical images of a Zr-based metallic glass after four stages: 1) as-cast; 2) after a first blasting step; 3) after an oxidation step; and 4) after a second blasting step. As shown in FIG. 4A, the as-cast texture of a metallic glass is that of a machined or cast surface. Generally, blasting can increase the surface roughness of the metallic glass. Further, porosity increases from the as-cast surface, as shown in FIG. 4A when compared to the first blasted surface (by shot media ZrO₂) shown in FIG. 4B, or the blasted surface after oxidization shown in FIG. 4D. The porosity microstructure can be used to darken the structural color of the metallic glass surface. The surface after blasting, as shown in FIG. 4B, is darker than the as-cast surface shown in FIG. 4A. The porosity remains after oxidization, as shown in FIG. 4C, when compared to the first blasted surface shown in FIG. 4B. As can be observed in FIG. 4D, the second blasting after oxidization can result in a more smooth and porous surface than the surface after oxidization shown in FIG. 4C.

The porous structure after oxidization shown in FIG. 4C is not observed on an oxidized Zr-based metallic glass surface without the first blasting step, as shown in FIGS. 5A-B. FIG. 5A shows an optical image of an oxidized Zr-based metallic glass surface without any blasting. FIG. 5B shows a magnified optical image of FIG. 5A. The resulting value of L* in the L*a*b* color spectrum with a blasting step is lower than without a blasting step. Likewise, a* and/or b* can be reduced. The oxidized surface appears darker than the blasted surface. The reason for this is that light scattering may be efficiently caused by the microstructure of the oxide layer including granular growth, which may be good for low reflection of light. With blasting, the granular growth of crystals can spread from a nucleation point. Without blasting, the growth direction can be parallel to the depth direction.

To further modify color and texture, the second blasting after the oxidation step can provide additional darkening. FIGS. 6A-C show optical photos of outer appearance of three stages shown in in FIG. 3 including (1) a first blasting, (2) oxidization, and (3) a second blasting after oxidization.

In various aspects, one or both of a* and b* values can be closer to zero by controlling the second blasting step. By oxidizing a blasted surface, as shown in FIG. 6B, the surface becomes darker than the blasted surface without further oxidization as shown in FIG. 6A. By blasting after oxidization, the surface in FIG. 6C becomes even darker than the surface after oxidization without further blasting as shown in FIG. 6B. For example, the color after oxidization, as shown in FIG. 6B, has an L* value of less than 45, an a* value of between −2 and zero, and a b* value of between −4 and zero. The color after the second blasting step, as shown in FIG. 6C, has a slightly lower L* value than that shown in FIG. 6B, and an a* value of greater than zero and less than 2, and a b* value of greater than zero and less than 2.

Without wishing to be limited to any mechanism or mode of action, when accumulating the oxidized layer by oxidization, the b* value can be closer to zero. The surface in FIG. 6D becomes lighter after a second oxidization (e.g. the b* value is increased) when compared to the surface shown in FIG. 6C for a second blasting step. For example, the color of the surface shown in FIG. 6D has an L* value slightly higher than that shown in FIG. 6C, an a* value that remains unchanged, and an increased the b* value than that shown in FIG. 6C.

By repeating the blasting and oxidizing steps, the color of the surface can be darkened or lightened and the texture can also be modified, for example, such that the surface becomes porous.

The as-cast metallic glass surface can contain features such as voids, coldshuts, flowlines, and misruns. Blasting can reduce these features. In further variations, the methods described herein can be used to improve or smooth surface features resulting from the combination of the blasting and oxidizing method described herein. In various aspects, the presence of surface features such as voids and crystalline particles can be reduced and/or concealed.

FIGS. 7A-D depict blasting and oxidation for reducing or removing crystals from a Zr-based metallic glass surface by using ZrO₂ sphere shot media. A first panel, as shown in FIG. 7A, depicts a crystal 704 on a metallic glass surface 702. A second panel, as shown in FIG. 7B, depicts the metallic glass surface after a one minute ZrO₂ blasting step, where the crystal 704 was removed on the surface 702. A third panel, as shown in FIG. 7C, depicts the surface after oxidation, where the crystal 704 was also removed on the surface 702. A fourth panel, as shown in FIG. 7A, depicts the surface after a second ZrO₂ blasting step, where the crystal 702 was removed on the surface.

FIGS. 8A-D depict blasting and oxidation for reducing or removing micro-voids from a Zr-based metallic glass surface. The blasting shot media was ZrO₂. A first panel, as shown in FIG. 8A, depicts micro-voids 804 on a metallic glass surface 802. A second panel, as shown in FIG. 8B, depicts the metallic glass surface after a one minute ZrO₂ blasting step, where the micro-voids 804 were removed. A third panel, as shown in FIG. 8A, depicts the surface after oxidation, where the micro-voids 804 were also removed. A fourth panel, as shown in FIG. 8D, depicts the surface after a second ZrO₂ blasting step, where the micro-voids 804 were also removed.

FIGS. 9A-D depict the blasting and oxidation steps for reducing shedding parts from a Zr-based metallic glass surface. Again, the blasting shot media was ZrO₂. A first panel, as shown in FIG. 9A, depicts a shedding part 902 on a polished metallic glass surface. A second panel, as shown in FIG. 9B, depicts the metallic glass surface after a one minute ZrO₂ blasting step, in which the shedding part 902 on the metallic glass surface was reduced. A third panel, as shown in FIG. 9C, depicts the surface after oxidation and a further reduction of the shedding part 902. A fourth panel, as shown in FIG. 9D, depicts the metallic glass surface after a second ZrO₂ blasting step, where the shedding part 902 was reduced still further. Shedding can be further reduced with additional blasting and oxidation steps.

FIG. 10A depicts an SEM image of the microstructure of the oxide layer formed after oxidization. As shown, fine equiaxed oxide crystals can be formed at the surface and grow down through the metallic glass matrix as columnar structures with a preferential growth direction. The microstructure in the thin surface region can be changed to a porous structure (e.g. dendrite crystal) by a first blasting or a preliminary blasting, which ensures the stability and strength of the oxide layer on the metallic glass surface.

FIG. 10B depicts microstructural analysis of the metallic glass surface of FIG. 10A by X-ray diffractometry. As shown in FIG. 10B, significant broadening of the tetra ZrO₂ (111) peak was observed after the secondary blasting step compared to the peak just after oxidization. The peak broadening suggests inhomogeneous strain introduction and implies formation of small amount of monoclinic-ZrO₂. Monoclinic-ZrO₂ can be formed by stress induced phase transformation of tetra-ZrO₂. This mechanism can be used for strengthening of ZrO₂ ceramics by stopping cracks.

In addition, a small peak shift to a lower angle of tetra-ZrO₂ (111) for the second blasted sample suggests an increased lattice parameter (i.e. expanding volume of the metallic glass). Without wishing to be held to mechanism or mode of action, the compressive residual stress can also strengthen the oxidized layer.

In some embodiments, a total processing time including blasting and annealing is greater than 2000 seconds, alternatively greater than 2500 seconds, alternatively greater than 3000 seconds, alternatively greater than 3500 seconds, or alternatively greater than 4000 seconds.

In various embodiments, the L*, a*, and/or b* color values can be controlled in accordance with the embodiments of the disclosure. For instance, the a* and b* values can be greater than or equal to −20, alternatively greater than or equal to −15, alternatively greater than or equal to −10, alternatively greater than or equal to −5, alternatively greater than or equal to −4, alternatively greater than or equal to −3, alternatively greater than or equal to −2, or alternatively greater than or equal to −1. Further, the a* and b* values can be less than or equal to 20, less than or equal to 15, less than or equal to 10, less than or equal to 5, alternatively less than or equal to 4, less than or equal to 3, less than or equal to 2, or less than or equal to 1. In various aspects, the L* value can be less than or equal to 75. In various aspects, the L* value can be less than or equal to 50. Alternatively, the L* value can be less than or equal to 45. Alternatively, the L* value can be less than or equal to 40. Alternatively, the L* value can be less than or equal to 35. Alternatively, the L* value can be less than or equal to 30. In various aspects, the L* value can be greater than or equal to 20. Alternatively, the L* value can be greater than or equal to 25. Alternatively, the L* value can be greater than or equal to 30. Alternatively, the L* value can be greater than or equal to 35.

Thermal Spray Blasting and Controlled Cooling

In a further aspect, the disclosure provides systems and methods for thermal spray blasting a metallic glass surface combined with controlled cooling. The systems and methods can be used to control surface appearance, including color hue and texture. The resulting metallic glass material is also provided.

Thermal spray blasting is able to create a thick oxide layer and a random surface texture on metallic glass material. In various aspects, the surface is modified within a very short time, e.g., approximately 30-60 seconds. When the surface texture becomes random, light reflection is reduced and thus the L* value of the metallic glass surface can be reduced.

Further, an additional oxidation step need not be taking in order to generate an oxide layer at the surface of the metallic glass. Instead, thermal spray blasting combines blasting and oxidization in a single step. In other words, the blasting and oxidization occur simultaneously in thermal spray blasting.

In certain embodiments, the thermal spray blasting can be generated by high velocity oxygen fuel (HVOF) or high velocity air fuel (HVAF) thermal spray systems. Thermal spray blasting parameters can be varied to obtain a desired surface modification and appearance. For example, combustion parameters, scan pattern and speed, type of shot media impacting the surface, intensity of blasting beam, and other conditions known in the art can be modified to control temperature and surface modification. Temperature can be controlled using, e.g., spray cooling of the thermal spray and the surface of the metallic glass. In certain embodiments, the temperature of the thermal spray and the blasted surface is additionally controlled, at least in part, by controlling the combustion parameters and the scan pattern and speed of the thermal spray. In some embodiments, temperature is further controlled by a temperature-controlled sample holder.

In certain aspects, thermal spray blasting a metallic glass surface with controlled cooling can provide an oxidized surface modification in the surface treated metallic glass material. The oxidized surface modification can control the appearance of the metallic glass material, including, e.g., color and texture of the metallic glass surface. By way of example and without limitation, dark (e.g., black) colored surfaces can be achieved by the thermal spray blasting methods with controlled cooling as described herein.

Without wishing to be held to a particular mechanism or mode of action, thermal spray blasting of the surface of a metallic glass with controlled cooling can form a surface oxide layer. In certain embodiments, the surface of the metallic glass is at least partially melted during the thermal spray blasting, resulting in impregnation of the blasted surface with blasting media. Further, thermal spray blasting can create a minimally impacted surface region containing shear bands or a supercooled liquid region due to a high temperature gradient. In certain aspects, the controlled cooling serves to quench the blasted surface below oxidation for sufficient vitrification. The diffusibility in shear bands is high, and therefore oxidization into the metallic glass surface area can be accelerated, thus reducing processing time.

Again, without wishing to be held to a particular mechanism or mode of action, the thermal spray blasting can create a distinct temperature gradient on the blasted surface region due to the high temperature of the flame. As such, sufficient cooling and temperature control is used for vitrification of the melted region on the surface of the metallic glass. The systems and methods of the disclosure, including thermal spray blasting and controlled cooling, therefore, can realize a combination of superheating, blasting and super cooling to provide modified metallic glass surface.

In various aspects, thermal blasting is performed using a shot media. The size, morphology, and material of the shot media can be selected and controlled to provide the desired surface modification. For instance, the shot media can be a high melting temperature material that does not partially or completely melt during thermal spray blasting. In certain embodiments, the shot media is a fine, e.g., having a median size between 10-100 μm, alternatively 10-45 μm. In certain embodiments, the shot media is a Zr-based, such as ZrO₂ shots or beads.

In certain embodiments, the thermal spray flame can be generated to provide any suitable temperature at the metallic glass surface. For instance, depending on the specific materials of use, the thermal spray flame can provide a temperature at the metallic glass surface of between 200° C. to 400° C., or alternatively between 250° C. and 350° C.

The methods described herein can be performed using any suitable system. By way of example, in certain embodiments, a system for thermal spray blasting of a surface with controlled cooling can include a thermal spray gun with integrated spray cooling in the flame nozzle, and a sample holder in operational alignment with the thermal spray gun. The system can further include at least one, two, three, or four spray cooling components exterior to the thermal spray gun. In certain embodiments, the thermal spray gun positioning and movement can be controlled by a programmable robotic arm. In other embodiments, the sample holder can be a temperature-controlled sample holder. The system can further include thermocouples to monitor temperature at various locations within the system.

Metallic glasses treated in accordance with the methods described herein are also provided. In certain embodiments, the metallic glass has an inconsistent oxidized surface morphology. By way of example, the inconsistent oxidized surface morphology exhibits rough surface variations having a depth of about 5-20 μm. The surface roughness can be measured by laser microscopy.

Various embodiments are discussed below with reference to FIGS. 11-14. However, those skilled in the art will readily appreciate that the detailed description given herein with respect to these Figures is for explanatory purposes only and should not be construed as limiting.

With reference to FIG. 11A, in accordance with certain aspects of the disclosure, a system 1100 is illustrated, including a thermal spray system 1102, e.g., an HVOF thermal spray system, and spray cooling system 1104, e.g., a water mist spray cooling system. In accordance with certain embodiments, the spray cooling directly reduces the temperature of the thermal spray flame by using, e.g., a mist water nozzle 1104 a set inside the combustion nozzle 1102 a in thermal spray gun. Additional mist sprays 1104 b, which cool the blasting substrate, can also be included for quenching after the thermal spray blasting. Further, a temperature controlled sample holder 1106 can be included to provide additional temperature control. In various aspects, the blasting angle can be perpendicular to the sample. Alternatively, the blasting angle can vary at an angle from perpendicular with the sample.

Thermal spray blasting parameters can be varied to obtain a desired surface modification and appearance. In certain embodiments, the thermal spray can be generated with various blasting parameters so as to control temperature of the thermal spray flame. By way of example, the combustion parameters, scan pattern and scan speed, type of shot media impacting the surface, intensity of blasting beam, and other conditions known in the art can be varied to achieve desired temperature control. In certain embodiments, the scan pattern can be generated with and without sample overrun to increase or decrease temperature at the surface of the metallic glass (discussed further below).

In other embodiments, the scan speed and frequency can be varied to increase or decrease temperature at the surface of the metallic glass. For instance, scan speeds can range from 25 mm/s to 200 mm/s, for example 50 mm/s to 100 mm/s. The temperature on the metallic glass surface increases with the scan speed increases. Further, scan frequency can range from 5 cycles to 25 cycles, for example 10 cycles to 20 cycles. The blasting cycle does not affect the surface temperature, but affects the surface smoothness. When the number of blasting cycles increases, the blasted surface becomes smoother. FIG. 11B illustrates example scanning patterns for thermal spray blasting. Two sample scanning paths are illustrated, one scanning path with sample overrun 1112 and one scanning path without sample overrun 1114 to change the heating effect of the thermal spray. Separately, the distance between the thermal spray gun and sample can be varied to change the heating effect of the thermal spray. For instance, the distance can be set between 200-500 mm, for example 300 mm.

The L*, a*, and/or b* color values can be controlled in accordance with the methods of the disclosure. For instance, the a* and b* values can greater than or equal to −20, alternatively greater than or equal to −15, alternatively greater than or equal to −10, alternatively greater than or equal to −5, alternatively greater than or equal to −4, alternatively greater than or equal to −3, alternatively greater than or equal to −2, or alternatively greater than or equal to −1. Further, the a* and b* values can be less than or equal to 20, less than or equal to 15, less than or equal to 10, less than or equal to 5, alternatively less than or equal to 4, less than or equal to 3, less than or equal to 2, or less than or equal to 1.

In various aspects, the L* value can be less than or equal to 75. In various aspects, the L* value can be less than or equal to 50. Alternatively, the L* value can be less than or equal to 45. Alternatively, the L* value can be less than or equal to 40. Alternatively, the L* value can be less than or equal to 35. Alternatively, the L* value can be less than or equal to 30. In various aspects, the L* value can be greater than or equal to 20. Alternatively, the L* value can be greater than or equal to 25. Alternatively, the L* value can be greater than or equal to 30. Alternatively, the L* value can be greater than or equal to 35.

In accordance with certain embodiments, the thermal spray blasting conditions can be varied so as to achieve desired color hue, e.g., a* values and/or b* values of less than 5 and or greater than −5, and L* values below 50. In various aspects, the a*and b* values can separately be greater than −5, greater than −4, greater than −3, greater than −2, or greater than −1. Alternatively, the a* and b* values can separately be less than 5, less than 4, less than 3, less than 2, and less than 1. In various aspects, the L* value can be less than 50. Alternatively, the L* value can be less than 45. Alternatively, the L* value can be less than 40. Alternatively, the L* value can be less than 35. Alternatively, the L* value can be less than 30.

For comparison, a non-blasted oxide surface shows an L* value of less than 40, an a* value below zero (e.g., −1 to −5), and b* value below zero (e.g., −5 to −15).

As an example, Sample 1 zirconium based metallic glass was prepared according to embodiments of the disclosure, and shows a dark color with the L*a*b* parameters having an L* value below 35, an a* value near zero, and a b* value near zero. Thermal spray operating parameters utilized to generate Sample 1 included a ZrO₂ blast media included a ZrO₂ blast media (e.g. Z10-45/10 by Fuji), and a scan speed of 50 mm/s for 10 cycles with pattern overrun. The resulting thermal spray achieved a temperature of about 270° C. on the surface of the metallic glass. The temperature can be measured by using a thermal sensor, such as a radiation thermometer.

As another example, Sample 2 zirconium based metallic glass was prepared according to embodiments of the disclosure. Sample 2 was prepared with a modified scan speed and pattern to eliminate scan overrun and to increase the heating effect. Thermal spray operating parameters utilized to generate Sample 2 included a ZrO₂ blast media (e.g. 210-45/10) and a scan speed of 100 mm/s for 10 cycles without pattern overrun. The resulting thermal spray achieved a temperature of about 370° C. Under these operating parameters, Sample 2 was bent by both softening above the glass transition and strong HVOF blasting forces. Sample 2 showed a dark color with L*a*b* parameters having an L* value below 35, an a* value of less than 5 and greater than −5, and a b* value of less than 5 and greater than −5. Compared to Sample 1, Sample 2 exhibited a slightly higher L* value and a* and b* values near zero.

Following the observed bending of Sample 2, a support plate was added to the system behind the sample to suppress bending. For example, an example Sample 3 was prepared according to embodiments of the disclosure with a reduced temperature of the HVOF flame to avoid excessive heating. Thermal spray operating parameters utilized to generate Sample 3 included a ZrO₂ blast media (e.g. Z10-45/10) and a scan speed of 100 mm/s for 10 cycles without pattern overrun. The resulting thermal spray achieved a temperature of about 310° C. Sample 3 showed a good black color with the L*a*b* parameters having an L* value below 35, an a* value of less than 5 and greater than −5, and a b* value of less than 5 and greater than −5. Compared to Sample 1 and Sample 2, Sample 3 exhibited a mid-range L* value, an a* value nearer Sample 1, and a slightly positive b* value of less than 5 and greater than −5.

Sample 4 depicts a zirconium based metal glass prepared with an increased number of thermal spray blasting cycles. The blasted surface of Sample 4 became smoothed, revealing a slightly blue-black color variation. Thermal spray operating parameters utilized to generate Sample 4 included a ZrO₂ blast media (e.g. Z10-45/10) and a scan speed of 100 mm/s for 20 cycles without pattern overrun. The resulting thermal spray achieved a temperature of about 370° C. A back support plate supported the metallic glass.

Sample 4 showed a dark color with the L*a*b* parameters having an L* value below 35, an a* value of less than 5 and greater than −5, and a b* value of less than 5 and greater than −5. Compared to other samples, Sample 4 exhibited a slightly higher L* value, an a* value of less than 5 and greater than −5, and a slightly more negative b* value of less than 5 and greater than −5.

In all cases, HVOF blasting dramatically reduced the time for oxidization-related black coloring treatment of Zr-based metallic glasses (e.g. about 30 seconds) compared with processes of blasting and oxidization by annealing (e.g. a total processing time greater than 3000 seconds or 50 minutes). Dark color L*a*b* parameters were obtained for all samples. In some embodiments, the blasting time is less than 2 minutes, alternatively less than 1 minute, alternatively, less than 50 seconds, alternatively less than 40 seconds, alternatively less than 30 seconds, alternatively less than 20 seconds, or alternatively less than 10 seconds.

In accordance with certain aspects of the disclosure, FIGS. 12A-12B show schematic illustrations which depict the effect of thermal spray blasting. As illustrated, the process is characterized by a combination of simultaneous blasting and oxidizing. FIG. 12A depicts thermal spray blasting 1202 generating a temperature at the metallic glass surface 1204 below Tg. As shown, below Tg, blast-introduced shear bands 1206 are formed that act to increase the diffusibility of gas 1208 into the blasted metallic glass matrix 1210. The depth and degree of improved diffusibility can be controlled, e.g., by the size and type of shot media. In addition, spray cooling mist can lead to the formation of hydroxides, which generate a porous oxide layer 1212 on the metallic glass surface 1204. Furthermore, as illustrated in FIG. 12B, when thermal spray blasting 1202 is continued and generates a temperature at the metallic glass surface 1204 above Tg, the surface region can be a supercooled liquid state 1214.

The thermal spray blasting described herein can cause high-speed heating of the surface of the metallic glass. When performed with the high scan speeds described herein in combination with cooling control, the temperature gradient of the blasted region in the depth direction becomes steeper. This steep temperature gradient is quite important for creating a surface melted region in the supercooled liquid state (above Tg, but not yet crystallized). In accordance with certain aspects of the disclosure, it has been found that thermal spray blasting above Tg leads to significant splashing and generates a random surface morphology. Specifically, the surface becomes random, reducing light reflection and decreasing the L* value of the metallic glass.

In accordance with certain aspects of the disclosure, during thermal spray blasting, a distinct flashing at or near the surface of the metallic glass can be observed, which indicates that the surface region is heated above Tg, causing splashing and burning (rapid oxidation) of the resulting metallic glass droplets. This phenomenon can result in the roughened surface observed on the blasted surface of the metallic glass samples.

In accordance with certain aspects of the disclosure, the systems and methods can alter the metallic glass at temperatures below Tg and above Tg. However, given the speed and intensity of the process, the resulting high-speed heating and cooling can effectively suppress crystallization and structural relaxation of the metallic glass. By using thermal spray blasting and cooling conditions, oxidized black-colored metallic glass, such as Zr-based metallic glasses, can be generated without substantial embrittlement due to structural and microstructural changes.

By way of example, with reference to FIGS. 13C-13D, cross sectional images of Sample 3 described above reveal a random surface morphology. As illustrated in FIGS. 13C-13D, a rough surface with surface variations having a depth of about 5-20 μm, e.g., 10 μm, is observed, though the oxide layer thickness is not consistent. The random morphology of this surface is indicative of the high temperature state (supercooled liquid above Tg) of the surface during thermal spray blasting. For comparison, FIGS. 13A-13B illustrate an oxidized surface created through a combination of blasting and annealing. As can be seen in FIGS. 13C-13D, the rough surface morphology and uneven oxide layer thickness of the metallic glass material subjected to thermal spray blasting with controlled cooling is not observed in the oxidized surface of the metallic glass material subjected to a combination of blasting and annealing.

In some embodiments, after a combination of blasting and oxidization, the metallic glass can have an inconsistent oxidized surface that exhibits rough surface variations having a depth of equal to or less than 20 μm, alternatively equal to or less than 15 μm, or alternatively equal to or less than 10 μm. In some embodiments, the metallic glass can have an inconsistent oxidized surface that exhibits rough surface variations having a depth of equal to or greater than 5 μm, alternatively equal to or greater than 10 μm, or alternatively equal to or greater than 15 μm.

Dissimilar Shot Blasting

The disclosure also provides a method of using a combination of different shot types during blasting, referred to herein as dissimilar shot blasting. The dissimilar shots can result in control of hue color, and can provide different impacts on complementary and structural color. In various aspects, dissimilar shot blasting media includes both large shot media and fine shot media. The combination of media provides for different material properties on the same metallic glass.

Without wishing to be limited to a particular effect or mode of action, large shot media (e.g. shot media average size between 100 μm and 2000 μm) has a larger impact and makes a deeper residual compressive stress in the metallic glass than fine shot media. In contrast, fine shot media (e.g. shot media average size between 10 μm and 100 μm) can create thin blast-impacted region on the surface. In addition, the density, shape, and stiffness of the shot material are important factors that allow control of the texture and structure of blasted surface. Blasting using dissimilar blast shot media can provide additional control of dark color of the metallic glass, such as in Zr-based metallic glasses, by oxidizing the blasted metallic glass surface. The blasting system and method are similar to that disclosed earlier by a combination of blasting and oxidization described herein.

In some aspects, large shot media can include sphere shaped base particles with sharp vertex. In some aspects, the sphere shaped particles can include a softer base material such as rubber, into which sharp harder components such as ceramics are embedded. The large shot media with sharp harder component can produce the microstructure observed in a supper black Ni-based metallic glass.

FIG. 14 shows the surface structure of a dark Ni-based metallic glass obtained with a chemical etching treatment. The black Ni-based metallic glass has certain L*, a*, and b* values of color space, i.e. an L* value of less than 10, an a* value of less than 1 and greater than −1, and a b* value of greater than −1 and less than 0. When the L*, a*, and b* values are nearly zero, the color is substantially black. The microstructure surface of the black Ni-based metallic glass is characterized by existence of deep-sharp indentation marks. This surface structure provides a structural color of the black Ni-based metallic glass.

In order to fabricate the black color and the surface texture as shown in FIG. 14, the shape of an example of a sphere shaped rubber based shot medium is shown in FIG. 15. The rubber based shot media 1502 creates mass for blast energy and stiffness for the lifetime of the shot. A ceramic material 1504 partially embedded in and protruding from the sphere shaped rubber base 1502 has a sharp vertex, such as vertex SiC media. In some embodiments, the shot media may have no vertex but can have a diamond coating. In some aspects, the diamond coating may be suitable for polishing surface. The vertex is configured to make deep/sharp indentation marks on a blasted surface. It will be recognized that the ceramic material can be selected from any ceramic known in the art. In some aspects, the ceramic is made of SiC, which is low cost and has sharp vertex. Any ceramic known in the art can be used. In some aspects, the large shot media can be Sirius #320 (Fuji Manufacturing). Because the large shot media has sufficient mass or weight to achieve high energy for blasting, the weight of SiC blasting media can be increased by combining SiC with a resin. Furthermore, the resin can have a damping effect for suppression of breakage of SiC particles.

Without wishing to be held to a particular mechanism or mode of action, the greater the mass, size, and shape of the base and protruded protrusion of large shot media such as that depicted in FIG. 15, the greater the indentation of the shot on the metallic glass. It will be appreciated by those skilled in the art that the shape and size and the materials including base 1502 and protruded portion 1504 of the shot media can vary depending upon the depth of the indentation desired for a blasted surface.

In various aspects, blasting using large shot media on a Zr-based metallic glass can have any incident angle. In many aspects, the incident angle of shot media can be at a right angle or nearly a right angle with a slight deviation of about 2 degrees from the surface. Blasting can be performed at room temperature, or a variation of temperatures.

In some aspects, the gas pressure of the blasting beam can be at least 0.3 MPa. In some aspects, the gas pressure is at least 0.4 MPa. In some aspects, the gas pressure is at least 0.5 MPa. Such pressures can create a deeper or sharper indentation on the metallic glass surface.

In various aspects, the blasting time for the large shot media or the fine shot media can be at least 5 minutes. In various aspects, the blasting time can be at least 7 minutes. In various aspects, the blasting time can be at least 9 minutes. In various aspects, the blasting time can be at least 11 minutes. In various aspects, the blasting time can be at least 13 minutes. In various aspects, the blasting time can be at least 15 minutes.

FIG. 16A shows a SEM image of the outer appearance of the surface of a Zr-based metallic glass blasted using large shot media (Sirius #320). FIG. 16B shows an example of the surface structure and texture of the metallic gas when treated with blast media at various gas pressures. As shown, the highest gas pressure of 0.5 MPa created deeper and shaper indentation marks than when blasting proceeded at lower gas pressures (e.g. 0.15 MPa and 0.3 MPa). As shown in FIG. 16C, the depth of indentation is as deep as 3.658 μm when a gas pressure of 0.5 MPa and two blasting passes were applied to the metallic glass. The depth of indentation is as deep as 1.981 μm with a gas pressure of 0.16 MPa and two passes applied to the metallic glass, while the depth is as deep as 1.562 μm with a gap pressure of 0.3 MPa and two passes applied to the metallic glass.

FIG. 17A shows that more metallic glass can be removed at an increased depth by using large shot media. FIG. 17A shows an optical image of the metallic glass surface blasted by using large shot media (Sirius #320). FIG. 17A also shows a cross sectional depth profile along the respective lines on the image. For example, point [1] has a depth of 0 μm, point [2] has a depth of 3.934 μm, point [3] has a depth of about −5 μm, and point [4] has a depth of about zero μm. The distance between point [2] and point [4] is 15.422 μm. The surface roughness can be measured by laser micro scope.

FIG. 17A also shows a predicted cross-sectional image of a metallic glass by using the large shot media. A deep indentation layer 1702 is formed on the surface of a metallic glass 1704. As shown, a surface roughness Rz of the metallic glass 1704 is about 7 μm, which indicates that the combination of large shot media and a high gas pressure can make a deep profile of residual stress. The presence of shear bands is depicted in FIG. 17B. The deep indentation marks can provide for structural color and reduce light reflection.

Without wishing to be limited to a specific mechanism or mode of action, deep and coarse shear bands can be characterized by loose random packing of atoms. Loose random packing can increase the mobility of atoms and is an important structural factor for increasing chemical reactions, for example, oxidization. Both the density and distribution of shear bands can be adjusted for making a desired chemical reacted region on a blasted surface.

Dense shear bands formed in a blasted region can be obtained by blasting a small sized or fine shot media. To avoid the effect of contaminated/penetrated media on a metallic glass surface, a fine zirconia (ZrO₂) shot media that are sphere like particles without sharp vertex (e.g. B505 by Fuji) can be used. B505 may include ZrO₂, SiO₂, Al₂O₃, or CuO among others.

FIG. 18A shows an optical image of the fine Zr-based blasting media metallic glass surface and a corresponding cross sectional depth profile along the lines on the optical image. As shown, the maximum value of surface roughness Rz is about 2 μm, which is about the same value as the as-cast state before the blasting, which indicates that the combination of small sized shot media and low gas pressure would make the very thin impacted region. As such, the shear bands would be condensed in a surface region with a depth of a few microns.

FIG. 18B shows the predicted cross-sectional image of a metallic glass blasted by using a second fine blasting shot media (e.g. B505). A layer of dense shear bands 1802 can be formed on the surface of the metallic glass 1704 by blasting with the fine blasting shot media (B505). The dense shear bands can have a thickness of about 2 microns. The dense shear bands can increase diffusibility and accelerate the growth rate of an oxide layer under oxidization. Therefore, this treatment using fine shot media is good for black color after oxidization as a result of forming a thick oxide layer. This surface treatment can promote surface oxidization, and accelerate oxide segregation at a grain boundary of an oxide layer. For instance, a complementary color by CuO (e.g. black color) might be assisted by using this surface treatment.

In accordance with certain embodiments, blasting with a combination of dissimilar shot media and oxidization can be varied so as to achieve desired color hue, e.g., an a* value and/or a b* value of less than 3 and or greater than −3, and an L* value below 35. In various aspects, the a* and b* values can separately be greater than −3, greater than −2, or greater than −1. Alternatively, the a* and b* values can separately be less than 3, less than 2, less than 1. In various aspects, the L* value can be less than 35. Alternatively, the L* value can be less than 30. Alternatively, the L* value can be less than 25.

For comparison, a non-blasted oxide surface has an L* value of less than 40, and an a* value close to zero (e.g., −1 to −5), and a negative b* value below zero (e.g., −5 to −15).

The combination of the two dissimilar blasting media can make a deep black color. FIG. 19 shows a predicted blasted profile by using a combination of fine blasting shot media (e.g. B505) and large shot media (e.g. Sirius #320). The profile includes the dense shear band layer 1802 over the deep indentation layer 1702. The blasted metallic glass surface is then oxidized. The large shot media can reduce only the L* value, but does not affect the b* value, when compared to an oxidized Zr-based metallic glass without blasting. In contrast, the fine blasting shot media can reduce both the a* and b* values to be nearly zero, while the L* value remains unchanged when compared to an oxidized Zr-based metallic glass without blasting. With the combination of the blasting media B505 and blasting media Sirius #320 before oxidization, a deep black color is created.

By way of example and not limitation, the black color has an L* value below 30, an a* value of greater than −2 and less than 2, and a b* value of greater than −15 and less than 15 for a blasted Zr-based metallic glass surface by using the large shot media Sirius #320.

A dark color has an L* value below 45, an a* value of greater than −2 and less than 2, and a b* value of greater than −2 and less than 2 for a blasted Zr-based metallic glass surface by using B505. By way of example and not limitation, the color is lighter than the blasted Zr-based metallic glass surface using the large shot media Sirius #320.

A dark color with an L* value below 35, an a* value of greater than −1 and less than 1, and a b* value of greater than −1 and less than 1 for a blasted Zr-based metallic glass surface by using a combination of large shot media Sirius #320 and fine shot media B505. The color is lighter than the blasted Zr-based metallic glass surface by using Sirius #320, but is darker than the blasted Zr-based metallic glass surface by using B505.

Compared to the single blasting by large shot media or the single blasting by fine media, the combined blasting of both large shot media and fine shot media provides a reduced L* value and a b* value closer to zero than the blasted metallic glass surface by using the fine shot media with a first blasting step and a second blasting step as illustrated in FIG. 3, an L* value of less than 40 and a b* value of less than 2 or greater than −2 can be obtained. The L* value of less than 40 of the fine shot media with a first blasting step and a second blasting step is higher than an L* value of 35 for the blasted surface by using the combination of dissimilar shot media. The b* value of less than 2 or greater than −2 of the fine shot media with a first blasting step and a second blasting step is larger than a b* value of 1 or greater than −1 for the blasted surface by using the combination of dissimilar shot media.

The combination of dissimilar shot blasting provided a darker surface color. For example, a deep black color of Zr-based metallic glass (e.g. LM105) can be created by blasting a combination of fine blasting shot media (e.g. B505) and another large blasting shot media (e.g. Sirius #320). The fine blasting shot media can reduce the b* value to be nearly zero (e.g. a b* value between −1 and 1), while the large shot media Sirius #320 can reduce the L* value toward nearly zero (e.g. an L value below 35).

In some embodiments, a total processing time including blasting and annealing is greater than 2000 seconds, alternatively greater than 2500 seconds, alternatively greater than 3000 seconds, alternatively greater than 3500 seconds, or alternatively greater than 4000 seconds.

In alternative embodiments, the large shot media and the fine shot media can be premixed. The mixture of the dissimilar shot media can then be blasted on a metallic glass. In some embodiments, the method can include an additional oxidation step. The metallic glass can be first blasted by large shot media (e.g. Sirius #320), followed by fine size shot media (e.g. B505), then followed by oxidization of the blasted metallic glass surface.

In some embodiments, the sequence of the blasting the dissimilar shot media can be reversed. For example, the metallic glass can be first blasted by a fine shot media (e.g. B505), followed by large shot media (e.g. Sirius #320), then followed by oxidization of the blasted metallic glass surface.

In some embodiments, the fine media shot has a median size equal to or less than 100 μm, alternatively equal to or less than 90 μm, alternatively equal to or less than 80 μm, alternatively equal to or less than 70 μm, alternatively equal to or less than 60 μm, alternatively equal to or less than 50 μm, alternatively equal to or less than 40 μm, alternatively equal to or less than 30 μm, alternatively equal to or less than 20 μm. In some embodiments, the fine media shot has a median size equal to or greater than 10 μm, alternatively equal to or greater than 20 μm, alternatively equal to or greater than 30 μm, alternatively equal to or greater than 40 μm, alternatively equal to or greater than 50 μm, alternatively equal to or greater than 60 μm, alternatively equal to or greater than 70 μm, alternatively equal to or greater than 80 μm, alternatively equal to or greater than 90 μm.

The depth of the oxide layer can be strongly affected by alloy composition. In various aspects, the blasted oxide layer may have a depth varying from 2 to 4 μm. However, an increased depth of the oxide layer can help increase the darkness of the resulting surface color.

In some embodiments, after blasting by a combination of dissimilar shot media and oxidization, the metallic glass can have a consistent oxidized surface that exhibits rough surface variations having a depth of equal to or less than 10 μm, alternatively equal to or less than 8 μm, alternatively equal to or less than 6 μm, alternatively equal to or less than 4 μm, or alternatively equal to or less than 2 μm. In some embodiments, the metallic glass can have a consistent oxidized surface that exhibits rough surface variations having a depth of equal to or greater than 2 μm, alternatively equal to or greater than 4 μm, alternatively equal to or greater than 6 μm, or alternatively equal to or greater than 8 μm.

Metallic Glasses

The systems and methods described herein can be applicable to any suitable metallic glass known in the art. In some non-limiting aspects, the metallic glass can be based on, or alternatively include, one or more elements that oxidize, such as Zr, Ti, Ta, Hf, Mo, W and Nb. In some variations, the metallic glass includes at least about 30% one or more of Zr, Ti, Ta, Hf, Mo, W and Nb. In some variations, the metallic glass includes at least about 40% one or more of Zr, Ti, Ta, Hf, Mo, W and Nb. In some variations, the metallic glass includes at least about 50% one or more of Zr, Ti, Ta, Hf, Mo, W and Nb. In certain embodiments, the metallic glass can be based on, or alternatively include, Zr. In some variations, the metallic glass includes at least about 30% Zr. In some variations, the metallic glass includes at least about 40% Zr. In some variations, the metallic glass includes at least about 50% Zr. Similarly, the surface treated metallic glass material described herein as a constituent of a composition or article can be of any type.

The metallic glass can include multiple transition metal elements, such as at least two, at least three, at least four, or more, transitional metal elements. The metallic glass can also optionally include one or more nonmetal elements, such as one, at least two, at least three, at least four, or more, nonmetal elements. A transition metal element can be any of scandium, titanium, vanadium, chromium, manganese, iron, cobalt, nickel, copper, zinc, yttrium, zirconium, niobium, molybdenum, technetium, ruthenium, rhodium, palladium, silver, cadmium, hafnium, tantalum, tungsten, rhenium, osmium, iridium, platinum, gold, mercury, rutherfordium, dubnium, seaborgium, bohrium, hassium, meitnerium, ununnilium, unununium, and ununbium. In one embodiment, a metallic glass containing a transition metal element can have at least one of Sc, Y, La, Al, Ti, Zr, Hf, V, Nb, Ta, Cr, Mo, W, Mn, Tc, Re, Fe, Ru, Os, Co, Rh, Ir, Ni, Pd, Pt, Cu, Ag, Au, Zn, Cd, and Hg. Depending on the application, any suitable transitional metal elements, or their combinations, can be used.

Depending on the application, any suitable nonmetal elements, or their combinations, can be used. A nonmetal element can be any element that is found in Groups 13-17 in the Periodic Table. For example, a nonmetal element can be any one of F, Cl, Br, I, At, O, S, Se, Te, Po, N, P, As, Sb, Bi, C, Si, Ge, Sn, Pb, and B. Occasionally, a nonmetal element can also refer to certain metalloids (e.g., B, Si, Ge, As, Sb, Te, and Po) in Groups 13-17. In one embodiment, the nonmetal elements can include B, Si, C, P, or combinations thereof. Accordingly, for example, the alloy can include a boride, a carbide, or both.

In some embodiments, the metallic glass described herein can be fully alloyed. The term fully alloyed used herein can account for minor variations within the error tolerance. For example, it can refer to at least 90% alloyed, such as at least 95% alloyed, such as at least 99% alloyed, such as at least 99.5% alloyed, or such as at least 99.9% alloyed. The percentage herein can refer to either volume percent or weight percentage, depending on the context. These percentages can be balanced by impurities, which can be in terms of composition or phases that are not a part of the alloy. The alloys can be homogeneous or heterogeneous, e.g., in composition, distribution of elements, amorphicity/crystallinity, etc.

The metallic glass can include any combination of the above elements in its chemical formula or chemical composition. The elements can be present at different weight or volume percentages. Alternatively, in one embodiment, the above-described percentages can be volume percentages, instead of weight percentages.

In certain embodiments, the metallic glass can be zirconium-based. The metallic glass can also be substantially free of various elements to suit a particular purpose. For example, in some embodiments, the metallic glass can be substantially free of nickel, aluminum, titanium, beryllium, or combinations thereof. In one embodiment, the alloy or the composite is completely free of nickel, aluminum, titanium, beryllium, or combinations thereof.

The afore described metallic glasses can further include additional elements, such as additional transition metal elements, including Nb, Cr, V, and Co. The additional elements can be present at less than or equal to about 30 wt %, less than or equal to about 20 wt %, less than or equal to about 10 wt %, or less than or equal to about 5 wt %. In one embodiment, the additional, optional element is at least one of cobalt, manganese, zirconium, tantalum, niobium, tungsten, yttrium, titanium, vanadium and hafnium to form carbides and further improve wear and corrosion resistance. Further optional elements can include phosphorous, germanium and arsenic, totaling up to about 2%, or less than 1%, to reduce the melting point. Otherwise incidental impurities should be less than about 2% or less than 0.5%.

In some embodiments, the metallic glass can include a small amount of impurities. The impurity elements can be intentionally added to modify the properties of the composition, such as improving the mechanical properties (e.g., hardness, strength, fracture mechanism, etc.) and/or improving the corrosion resistance. Alternatively, the impurities can be present as inevitable, incidental impurities, such as those obtained as a byproduct of processing and manufacturing. The impurities can be less than or equal to about 10 wt %, about 5 wt %, about 2 wt %, about 1 wt %, about 0.5 wt %, or about 0.1 wt %. In some embodiments, these percentages can be volume percentages instead of weight percentages.

The disclosed methods herein can be valuable in the fabrication of electronic devices using a metallic glass-containing part. An electronic device herein can refer to any electronic device known in the art. For example, it can be a telephone, such as a mobile phone, and a land-line phone, or any communication device, such as a smart phone, including, for example an iPhone®, AppleWatch, and an electronic email sending/receiving device. It can be a part of a display, such as a digital display, a TV monitor, an electronic-book reader, a portable web-browser (e.g., iPad®), and a computer monitor. It can also be an entertainment device, including a portable DVD player, conventional DVD player, Blue-Ray disk player, video game console, music player, such as a portable music player (e.g., iPod®), etc. It can also be a part of a device that provides control, such as controlling the streaming of images, videos, sounds (e.g., Apple TV®), or it can be a remote control for an electronic device. It can be a part of a computer or its accessories, such as the hard drive tower housing or casing, laptop housing, laptop keyboard, laptop track pad, desktop keyboard, mouse, and speaker. The article can also be applied to a device such as a watch or a clock.

The methods can also be valuable in forming wearable metallic glass products that have a good cosmetic profile and do not readily degrade or show evidence of wear.

Any ranges cited herein are inclusive. The terms “substantially” and “about” used throughout this Specification are used to describe and account for small fluctuations. For example, they can refer to less than or equal to.±5%, such as less than or equal to ±2%, such as less than or equal to ±1%, such as less than or equal to ±0.5%, such as less than or equal to ±0.2%, such as less than or equal to ±0.1%, such as less than or equal to ±0.05%.

Having described several embodiments, it will be recognized by those skilled in the art that various modifications, alternative constructions, and equivalents can be used without departing from the spirit of the disclosure. Additionally, a number of well-known processes and elements have not been described in order to avoid unnecessarily obscuring the present disclosure. Accordingly, the above description should not be taken as limiting the scope of the disclosure.

Those skilled in the art will appreciate that the presently disclosed embodiments teach by way of example and not by limitation. Therefore, the matter contained in the above description or shown in the accompanying drawings should be interpreted as illustrative and not in a limiting sense. The following claims are intended to cover all generic and specific features described herein, as well as all statements of the scope of the present method and system, which, as a matter of language, might be said to fall therebetween. 

1. A method of altering a surface of a metallic glass, the method comprising: blasting the surface of the metallic glass with a shot media to form a porous blasted metallic glass surface having an oxidized layer having a first thickness; oxidizing the porous blasted metallic glass surface at an elevated temperature to form an oxidized metallic glass surface having an oxidized layer with a second thickness larger than the first thickness.
 2. The method of claim 1, further comprising blasting the oxidized metallic glass surface to form a modified metallic glass surface; and oxidizing the modified metallic glass surface to change color and texture of the modified metallic glass surface.
 3. The method of claim 1, wherein the shot media comprises ZrO₂.
 4. The method of claim 1, wherein the shot media has sizes from 10 μm to 100 μm.
 5. The method of claim 1, wherein the porous blasted metallic glass surface contains fewer surface features than the surface of the metallic glass before blasting.
 6. The method of claim 1, wherein the oxidized metallic glass surface has a roughness from 5 μm to 10 μm.
 7. A method of altering a surface of a metallic glass, the method comprising: blasting the surface of the metallic glass with a large shot media having an average diameter from 100 μm to 2000 μm; blasting the surface of the metallic glass with a fine shot media having an average diameter from 10 μm to 100 μm; and oxidizing the blasted surface of the metallic glass to form an oxidized metallic glass surface.
 8. The method of claim 7, wherein the large shot media comprises a polymer base and a protruded sharp ceramic vertex, and the fine shot media comprises fine round ceramic particles.
 9. The method of claim 7, wherein blasting with the large shot media and blasting with the fine shot media is simultaneous.
 10. The method of claim 7, wherein the oxidized metallic glass surface has a roughness from 2 μm to 10 μm.
 11. The method of claim 7, wherein a processing time of blasting with large shot media and fine shot media, and oxidizing, is greater than 3000 seconds.
 12. A method of treating a surface of a metallic glass, the method comprising: thermal spray blasting the surface of the metallic glass; and simultaneously with the thermal spray blasting, spray cooling the surface of the metallic glass, to form an oxide layer on the surface of the metallic glass.
 13. The method of claim 12, wherein a temperature of the surface of the metallic glass is further controlled using a temperature controlled sample holder.
 14. (canceled)
 15. The method of claim 12, wherein the thermal spray blasting proceeds for less than 2 minutes.
 16. The method of claim 12, wherein the thermal spray is produced using a high velocity oxygen fuel (HVOF) thermal spray system.
 17. The method of claim 12, wherein the thermal spray comprises a blasting media for blasting of the surface of the metallic glass.
 18. The method of claim 17, wherein the blasting media comprises ZrO₂ media.
 19. The method of 17, wherein the blasting media has sizes varying from 10-100 μm.
 20. The method of claim 12, further comprising blasting the surface of the metallic glass with a blasting media to control surface smoothness, porosity, or a combination thereof.
 21. The metallic glass of claim 12, wherein the oxidized surface includes a non-uniform oxidized surface that exhibits surface variations to a depth of about 5-20 μm. 22.-29. (canceled) 